Present work deals with an assessment of some physico chemical and biological characteristics of the river Cauvery and its tributary Arasalar in Kumbakonam area, Tamil Nadu, India. The study was carried out during the period from January 2010 to December 2010. Physico-chemical parameters like air temperature, water temperature, transparency, electrical conductivity, total solids, total dissolved solids, total suspended solids, pH, free carbon dioxide, dissolved oxygen, BOD, COD, Calcium, magnesium sodium, potassium, ammonia, nitrate, nitrite, phosphate, sulphate and silicate were carried out during the investigation period. Among the parameters, BOD values were not compiling with WHO guide lines in the river Cauvery and total solids and BOD values were not compiling with WHO guide lines in the river Arasalar. However, nutrients levels were low during the study period and did not give any clear seasonal variation. The results revealed that the values of nitrate and phosphate do not compile with WHO standards. Soil nutrients like phosphate, nitrate, potassium and sulphate showed no significant variation. The organic carbon and organic matter were higher concentration in the soil sediment. The present study also indicated that the distribution and abundance of phytoplankton and zooplankton were season dependent. The phytoplankton propagated more rapidly owing to its short turn over period whereas zooplankton was simple in composition and distribution. Ichthyofauna diversity reveals that a total of forty species and thirty five species belonging to seven orders, and fourteen families were identified in the river Cauvery and Arasalar respectively. However, the increasing anthropogenic pressures on the rivers adversely affected the fish production potentialities and they no longer support the rich biotic wealth. The present study concludes that the river Arasalar was severely polluted than Cauvery by anthropogenic performance due to local anthropogenic activities, agricultural runoff and discharge of untreated municipal sewage, religious credence and subject to seasons, climate and flows and influx of waters from various tributaries.